Liquid crystal display panels having a transverse electrical field mode, such as an In-Plane Switching (IPS) mode or a Fringe Field Switching (FFS) mode, have an advantage over known liquid crystal display panels having vertical electrical field mode (VA mode, for example) in that the viewing angle dependence of γ (gamma) properties is low. Hence, the use of such panels as small- and medium-sized liquid crystal display panels in particular is increasing.
However, as the resolutions of liquid crystal display panels increase, the pixel aperture ratios (a ratio of the total surface area of the pixel openings occupying the display region) decrease, and it is becoming difficult to achieve a satisfactory display luminance. Particularly in small- and medium-sized liquid crystal display panels for mobile applications, a drop in the contrast ratio when viewing in bright environments such as outdoors is a concern.
Thus far, the contrast ratio is increased by increasing the brightness of a backlight and by increasing the display luminance to deal with such a concern. However, increasing the brightness of the backlight may consume more energy, and responding by increasing the brightness of the backlight is nearing its limit.
Reflection by the liquid crystal display panel is one reason why the contrast ratio of the liquid crystal display panel drops in bright environments. Thus, attempts are being made to improve contrast ratios by reducing reflection by liquid crystal display panels.
For example, PTL 1 discloses an IPS mode liquid crystal display panel that prevents a situation in which light reflected by a liquid crystal cell is emitted to an observer side, by providing a phase difference plate (also referred to as a “front-side phase difference plate”) between a linear polarizing plate (also referred to as a “front-side linear polarizing plate”) disposed on the observer side (also referred to as a “front side”) and the liquid crystal cell. The front-side phase difference plate is provided so that linear polarized light transmitted through the front-side linear polarizing plate becomes circular polarized light that rotates in a first direction, and enters the liquid crystal cell. In other words, the front-side linear polarizing plate and the front-side phase difference plate function as a circular polarizing plate. When circular polarized light is reflected (at an interface where the refractive index changes from low to high), the phases of both P waves and S waves are shifted by n radian, and the rotation direction reverses as a result. Thus, light reflected in the liquid crystal cell (transparent substrate) becomes circular polarized light having the rotation direction of a second direction, which is the reverse of the first direction, and linear polarized light obtained from the circular polarized light passing through the front-side phase difference plate is absorbed by the front-side linear polarizing plate.
The liquid crystal display panel of PTL 1 further includes another phase difference plate (also referred to as a “rear-side phase difference plate”) disposed between a linear polarizing plate (also referred to as a “rear-side linear polarizing plate”) disposed on a backlight side (also referred to as a “rear side”) and the liquid crystal cell. The rear-side phase difference plate is configured so that linear polarized light transmitted through the rear-side linear polarizing plate becomes circular polarized light having a rotation direction that is the second direction, which is the reverse of the first direction, upon passing through the rear-side phase difference plate and a liquid crystal layer in a black display state. By passing through the front-side phase difference plate, the circular polarized light having the second direction as the rotation direction is transformed into linear polarized light to be absorbed by the front side polarizing plate. According to PTL 1, an IPS mode liquid crystal display panel capable of achieving good image quality even when used outdoors can be obtained.